need help planning out flow of trip

You can take a direct train from Geneva’s Airport to Lausanne (1h).
Lausanne to Zermatt requires a transfer (3h).
Zermatt to Lauterbrunnen (Berner Oberland) has three connections (2h 45m).
Lauterbrunnen to Bern has a connection (1h 30m).
There’s a direct train from Bern to St. Gallen (Appenzell) taking 2h 30m.
Two transfers are required from St. Gallen to Strasbourg (4h 30m).
Strasbourg to Baden-Baden (Black Forest) takes 30-minutes and is direct...
and there’s a direct train from Baden-Baden to Frankfurt (1h 30m).

Great destinations in the itinerary. However, with 2-3 days in Strasbourg, you only have 10 days in Switzerland. I don’t know if you were planning to overnight in all 5 destinations, but the 16 hours spent getting to them all is the equivalent of two whole days in the working world, and it’s time taken away from being able to enjoy where you go. You’ll enjoy Switzerland more if you pick 3- 4 locations to base at,
The Berner Oberland is definitely worth as many of the 10 days that you can carve out for it— 4 nights (3 days) is the minimum as there’s so much to see and do there. Because August is actually the rainiest month (12 days) around Lauterbrunnen, adding an extra day is a good idea there just in case a rainy day washes out the plans for the outdoors. Unless you’re a mountain climber, in August Zermatt has the Matterhorn but seeing it does not require overnighting in Zermatt. BTW: August also brings the rainiest month to Zermatt when there’s some rain on 24 days. That means if you go to Zermatt there’s a good chance the Matterhorn will be behind clouds and not visible. If you stay in Lausanne two nights and the Berner Oberland four nights, there are four nights remaining: two for Appenzell and two for Bern.

Here is a revised tentative plan: Lausanne 2 nights— See the Matterhorn on the way to Bern— Bern 2 nights- Appenzell 2 nights— Berner Oberland 4 nights. Strasbourg 3 nights.

If you really want to add a day or two so you can visit the Black Forest you will need more than 14 days for the trip.

Hi!

I agree with Kenko that you probably need to squeeze a destination, but I am not sure about the suggested order.
Bern is easy to visit as a day trip from Lausanne or from the Berner Oberland, so I would skip sleeping in Bern, and head to Strasbourg from Appenzell - otherwise keeping the same order of destinations as in your original post.
The ride from Interlaken to St. Gallen via Luzern and the 'Voralpen Express' will definitely tick the "scenic railway" box.
Attempting to see the Matterhorn as a (long) detour between Lausanne and Bern would have you spend most of the day on trains...

After reading balso’s post this flows better than what I suggested earlier:
Take a direct train from Geneva’s Airport to Lausanne (1h). From Lausanne take a day trip to Bern (1h 15m).
Lausanne to Zermatt requires a transfer (3h).
Zermatt to Lauterbrunnen (Berner Oberland) has three connections (2h 45m).
Lauterbrunnen to St. Gallen (Appenzell) has two changes (4h).
Two transfers are required from St. Gallen to Strasbourg (4h 30m).
Strasbourg to Baden-Baden (Black Forest) takes 30-minutes and is direct...
and there’s a direct train from Baden-Baden to Frankfurt (1h 30m).
I agree with kenko about spending a minimum of four nights in the Berner Oberland. I feel of all the places you want to see the Berner Oberland should be the priority. With Zermatt being the outlier I would skip it, especially since you don’t have the time to hang around in case you don’t see the Matterhorn on day one.

Great input. Thank you everyone. I am thinking we need to add on a couple of days if we want to do all this. Or remove Appenzell or Zermatt from the equation.

Depending on what all you want to do- have you considered Bern as a base for day tripping after Lausanne? We want to do a similar trip, and I just have us going out vs extra moving of hotels and ultimately back tracking to head up to Black Forest.